Field
The present disclosure relates to a lithium silicate crystalline or amorphous glass composition overlaying the top surfaces of zirconia and the manufacturing process of such products, more particularly to, a lithium silicate amorphous glass or lithium silicate crystalline glass composition with high light transmittance and good coloring characteristics and manufacturing processes of such products, which overlay the top surface of zirconia with high mechanical strength frameworks or copings.
Discussion of the Background
With increased interest in appearance from economic development and increased income, the aesthetic aspect of prosthetic dental materials gains high attention. This leads to the introduction to different kinds of prosthetic restoration materials with aesthetic functions, and also to the development of various non-metal restoration materials.
Dental ceramic materials for restoring a damaged tooth can be classified to a coping material for substructure, and aesthetic crowns depending on the material characteristic demands. Coping is a part of artificial teeth prosthesis that refers to a saddle-like covering placed on the top of abutments or a damaged tooth, on which crown materials similar to a dentin layer are placed.
Dental coping distributes and/or absorbs various occlusal loading transferred through a crown, thus requiring high mechanical properties. Common ceramic materials for coping include glass-infiltrated alumina, zirconia, and the like. Though it shows excellent value accuracy from near-net shape characteristics by infiltrating glass to preparatory porous alumina mold structures, glass-infiltrated alumina has low biaxial flexural strength, e.g., less than 450 MPa. Though it has an excellent mechanical property over 1200 MPa, zirconia has low light transmittance or poor coloring characteristics. Therefore, developments of these coping materials are focused on high light transmittance and good coloring characteristic with high shear modulus.
Crown materials refer to prosthetic materials for restoration of damaged teeth surfaces similar to dentin and enamel. Crown materials are classified into inlay, onlay, veneer, and crown depending on the area to which they are applied. Since crowns are applied to the outmost surfaces or teeth, not only aesthetic traits are highly necessary, but also high strength is demanded to endure chipping and/or wear against opposing dentition. Materials previously developed for crowns are leucite glass ceramics, reinforced porcelain, and fluorapatite (Ca5(PO4)3F) crystalline glass. Though they have high aesthetic traits, they are subject to fracture due to low flexural strength, e.g., around 80 to 120 MPa. Therefore, various crown materials with high strength are being developed.
Monolithic dental crown materials employing crystalline glass including lithium disilicate have been introduced. Though this crystalline glass may have high aesthetic traits, the mechanical strength of monolithic crown manufactured by the method is low around 300 to 400 MPa, which is not adequate for posterior teeth or bridges exposed to high stress.
Further, prosthetic materials reinforced by coating crystalline glass on the top of a zirconia substructure may be produced. More specifically, coating crystalline glass on the top of a zirconia substructure is characterized with the extension of the applicable area of crystalline glass by allowing its veneering on the top surfaces of zirconia. Unlike techniques which build up dentin by coating the top surfaces of zirconia with fluorapatite or porcelain powder, this method builds up dentin with aesthetic materials on zirconia by casting crystalline glass in an ingot shape at high pressure. However, the layer with aesthetic materials still has low strength with danger of fracture, which leads to continuing research on glass properties to overcome this problem.